1. Field of the Invention
The invention relates to an inflatable packer device, such as a packer, bridge plug, or the like, for use in a subterranean well bore, and a method of using same.
2. Description of the Prior Art
Inflatable packers, bridge plugs, and the like have long been utilized in subterranean wells. Such inflatable tools normally comprise an inflatable elastomeric bladder element concentrically disposed around a central body portion, such as a tube or mandrel. A sheath of reinforcing slats or ribs is typically concentrically disposed around the bladder, with a thick-walled elastomeric packing cover concentrically disposed around at least a portion of the sheath, typically a central portion of the sheath. Pressured fluid is communicated from the top of the well or interior of the well bore to the bore of the body and thence through radial passages, or around the exterior of the body, to the interior of the bladder.
Normally, an upper securing means engages the upper end of the inflatable elastomeric bladder and reinforcing sheath, sealably securing the upper end of the bladder relative to the body, while a lower securing means engages the lower end of the bladder and reinforcing sheath, sealably and slidably securing the lower end of the bladder for slidable and sealable movement on the exterior of the body, in response to the inflation forces.
With inflatable packers of this type, it has been observed that the exposed anchor section of the packer inflates prior to the other sections of the packer which are reinforced against expansion by an elastomeric packing cover element. When an exposed portion, such as the exposed anchor section of the bladder, inflates, the lower end of the bladder moves upwards relative to the body, and the exposed portion inflates until it meets the wall of the well bore, which may be cased or uncased. If well bore is uncased, the well bore will have a wall, and if the well bore is cased, the wall of the well bore will be the interior of the casing.
Although not fully understood, as the inflation begins to propagate downward and the reinforced portions of the bladder begin to inflate, the bladder has a propensity to pinch around the exterior of the body, creating a seal that prevents the effective communication of further fluid to the lower portions of the bladder. As the upper portion of the bladder above the seal continues to inflate, a convoluted fold forms in the bladder at the point of the seal, thus entrenching the seal.
The seal prevents or obstructs passage of the pressured fluid, employed for inflating the inflatable bladder, from reaching the lower portions of the bladder. Further, if the bladder is successfully inflated, the convoluted fold often remains in the bladder. During deflation, this fold can similarly pinch and seal around the body, obstructing the communication of fluid out of the lower portions of the bladder and thereby preventing complete deflation of the bladder.
Prior art packer devices have used the concept of shearably anchoring the slidable end of the bladder to the central body, so that the bladder is not free to immediately move axially in response to inflation forces produced by the introduction of pressured fluid to the interior of the bladder. This introduces a tensile load (or "pre-loading"), causing a predisposition to expand into the bladder, sheath, and cover, and also causes an annular gap to form between the interior of the bladder and the exterior of the central body, due to slight inflation of the bladder caused by the introduction of pressured fluid. The bladder is thus predisposed to expand when the amount of pressure in the bladder is achieved to shear the anchoring means, thereafter allowing full radial expansion of the bladder along its axial length. With this annular gap formed and preloading of the bladder, the tendency for the upper portion of the bladder to inflate prior to the lower portions thereof is reduced, thereby reducing the propensity of the bladder to pinch and seal on the body during the earliest stage of inflation. Examples of prior art incorporating such pre-loading can be found in U.S. Pat. Nos. 4,832,120 and 4,951,747.
Although the prior art methods predispose the bladder and the sheath and cover to inflate or radially expand, the shearable anchoring means allows no axial movement of the slidable end of the bladder until sufficient pressure causes the anchoring means to shear. Because the anchoring means prevents movement of the slidable end of the bladder and thus inflation of the bladder in this initial stage of the introduction of pressured fluid to the interior of the bladder, the amount of pressured fluid that can be introduced into the interior of the bladder is limited, as is the degree of initial inflation of the bladder and, correspondingly, the size of the annular gap formed and the degree of predisposition to expand.
The present invention addresses the pinching and sealing problems set forth above by providing an inflatable packer device and method of use which provides a tension means such as tensile bolts to allow the formation of a greater amount of uniformly distributed initial inflation fluid and the formation of a larger annular gap between the interior of the bladder and the exterior of the body, to further diminish the bladder's propensity to pinch and seal on the body once the tension means is released.